The Finnish champions saw off RFS in a nerve-wracking penalty shootout to advance, while the visitors begin their journey to the group stage in the second round.
Match preview
RFS midfielder Stefan Panic certainly defined the expression hero to zero in the Champions League first qualifying round, as HJK were taken all the way to penalties following a 2-1 second-leg loss after Manuel Martic had put his side in the ascendancy in Helsinki.
Panic netted the second of RFS' goals in the second leg but was then the only player who failed to convert from 12 yards in the shootout, as all five of HJK's takers made the net ripple to keep their continental journey in the top tier alive.
Toni Koskela's men have a bit of ground to make up in the 2022 Veikkausliiga if they are to defend their title but enter the first leg off the back of a 3-1 success over Vaasan Palloseura, but the second-round curse has bedevilled the hosts in the Champions League recently.
Indeed, the Finnish champions - who went all the way to the group stage in 1998-99 - have bowed out at that stage in the past three seasons and have never got past the third round of qualifying since the turn of the millennium.
Winning five of their last seven games at home does stand HJK in good stead ahead of the first leg, and Koskela's side - who were Europa Conference League group-stage participants last year - will at least have the consolation prize of a shot at Europa League qualification should they come out second best here.
Ending a four-year drought without a Czech First League title to their name, Viktoria Plzen finished one place below Slavia Prague in the regular season standings but stumped their authority on the Championship Group to get their hands on the trophy.
Michal Bilek's crop ultimately ended the campaign seven points clear of Slavia Prague after winning six of their final seven games, but the Czech champions endured a mixed bag of results in their recent pre-season friendlies.
Viktoria Plzen scored 15 goals across three friendly wins against Slovan Bratislava, Taborsko and Slavia Karlovy Vary, but they failed to triumph in any of their final three exhibition games with Botosani, Sint-Truiden and Besiktas.
The visitors endured a campaign without continental football last term after failing to make the Conference League group stage, but they have reached the Champions League proper on three previous occasions and are also out to end a run of consecutive second-round eliminations here.
HJK Helsinki Champions League form:
HJK Helsinki form (all competitions):
Viktoria Plzen pre-season form:
Team News
HJK Helsinki lost both David Browne and Pyry Soiri to injury in the second leg against RFS, although the former was fit enough to play a part off the bench on Saturday.
However, Soiri was not involved in any capacity and could be consigned to the treatment room alongside Roope Riski, Valtteri Moren, Miska Ylitolva and Manuel Martic.
Celtic loanee Conor Hazard ought to act as the last line of defence for HJK, while Malik Abubakari will hope to win the intense battle for the striker's spot, demoting Fabian Serrarens to the bench in the process.
Meanwhile, Viktoria Plzen centre-back Filip Kasa has made his recovery from knee surgery and was able to complete 30 minutes of the recent draw with Besiktas, but Petr Pejsa is still absent.
Kasa's fellow defender Lukas Hejda missed his side's final pre-season friendly with an ankle issue, but the 32-year-old is expected to be fit enough to marshal the defence here.
HJK Helsinki possible starting lineup:
Hazard; Peltola, Tenho, Hoskonen, Raitala; Vaananen, Hetemaj, Boujellab; Terho, Abubakari, Browne
Viktoria Plzen possible starting lineup:
Stanek; Reznik, Hejda, Pernica, Havel; Bucha, Kalvach; Cadu, Sykora, Mosquera; Chory
We say: HJK Helsinki 0-1 Viktoria Plzen
Despite not being the favourites on paper, HJK Helsinki have enjoyed regular competitive football over the past few weeks, while Viktoria Plzen may be feeling somewhat deflated after an underwhelming end to pre-season.